Maintaining the ban on same-sex marriage in Northern Ireland should not be used as a “veil for homophobia”, the Court of Appeal heard on Thursday.
Judges were told gays and lesbians have been wrongly excluded from legislation which allows those in the rest of the UK to wed.
Counsel for two couples challenging the prohibition made the claims after reasons for the current position were set out.
The legitimate aim, according to a Stormont department, is to preserve and promote the institution of marriage between a man and a woman.
But Grainne Close and her partner Shannon Sickles, along with Chris and Henry Flanagan-Kane, are seeking to overturn a ruling that the prohibition does not breach their human rights under European law.
In 2005 they became the first couples in the UK to enter civil partnerships, cementing their relationships in ceremonies at Belfast City Hall.
Last year a judge dismissed the case after finding that it was a matter for legislators rather than the courts.
Ms Close, Ms Sickles and the Flanagan Kanes claim they are being subjected to discrimination on the basis of their sexuality.
Prior to the collapse of devolution MLAs held five votes on the issue - with a narrow majority in favour of the move back on the last occasion in November 2015.
However, the DUP deployed a petition of concern mechanism to block the motion.
On day two of the case, counsel representing the Department of Finance detailed the position taken by former DUP ministers in statements to the Assembly.
Tony McGleenan QC told the court: “The legitimate aim can be characterised as the preservation and promotion of the institution of marriage in the form of a union between a man and a woman.”
Pressed by Lord Chief Justice Sir Declan Morgan, no evidence was produced of any adverse impact on traditional marriage since the 2013 Same Sex Couples Act was introduced in England and Wales.
He stressed how the secretary of state has the power to take action, but has chosen not to.
In closing submissions Ronan Lavery QC, for the couples, argued: “The 2013 Act is a game-changer, we now have a different definition of marriage in the UK.”
Excluding Northern Ireland from that cannot be justified, the barrister stressed.
“The context of all this should not be forgotten - a history of discrimination against gays and lesbians.
“They were described pejoratively as dykes and fruits, that continues to this day and its something we need to address.”
Proceedings were adjourned until later this month, for further arguments on Attorney General John Larkin QC’s claim the applicants lack legal standing to bring the action.